The thermal conductivity of transparent ceramics can be an important design parameter when components are to be used in situations and environments with fast temperature changes.In this work the thermal conductivity of undoped and Eu3+-doped lanthanum zirconate (La2Zr2O7) pyrochlore ceramics usable as luminescent materials are determined via the laser flash technique from room temperature to 700 °C.Using careful measurement and evaluation procedures, the thermal conductivity of dense (pore-free) La2Zr2O7 ceramics has been determined to be 3.01 W·m-1·K-1 at 25 °C, followed by a decrease to values around 2 W·m-1·K-1 at 400 °C and a slight increase towards 700 °C.Below 600 °C the thermal conductivity decreases with increasing 3+ concentration, as expected, but at 600 °C a crossover is observed and this trend is changed to the opposite.